electau

If you try to measure the earth electrode resistance to the general mass of earth the voltage of a multi meter 300mV may be insufficient to break down the initial contact resistance. However you can try using a short electrode in the ground located about 1 metre from the main earth electrode and measure between those two points. This saves you disconnecting the main earth connection.

The main objective is to make sure that the resistance is low enough to operate a RCD or RCBO when the TT or direct earthing system is used ie. no connection between the incoming supply neutral and main earth. A single 12.7mm copper clad steel electrode 1.2 metres into the general mass of earth will meet this requirement.

Indirect contact protection.

Maximum permissable earth resistance.

10mA RCD sensitivity Max earthing resistance 5000 ohms.

30mA RCD sensitivity Max earthing resistance 1666 ohms.

This measured value of earth resistance must be such that the product of this value and the RCD residual operating current does not exceed 50VAC.

Eg. 0.03mA x 1666 ohms = 50V.

An RCD will give protection from direct contact, but in this case the current flow to earth is through the human body. The touch voltage will be much higher ie it will be the supply voltage. A 30mA RCD will operate with a max resistance of 7666ohms on 230V.

For a 220 volt supply this will be 7333ohms.

An RCD is designed to operate and must operate in less than 0.4seconds.

TT or direct earthing resistance will never be low enough in ohms to operate an overcurrent device such as an MCB. This is why an RCD device must be used to protect against earth faults.

No problem Mate

It's important to remember that this board is populated by enthusiastic DIYers who may not fully understand the ramifications of what they're doing (exactly the type of people we're trying to discourage in the UK [and I assume Oz too]).

In the case of not knowing exactly what's installed (I like to actually look) we should recommend the lowest common denominator that ensures a reasonable level of safety without introducing potentially hazardous situations.

Keep up the good work, it's always nice to have alternative opinions and solutions

Thanks Crossy, the main issues as I see Thailand is short on are 1, Earthing, 2. Circuit protection and 3. Voltage drop on circuits.

Installing an MCB will protect the load side the 6 sqmm and 4sq mm conductors to the line side of the protective devices for airconditioners in the event of short circuit between L and N.

Service fuses are generally not fitted to protect consumers mains in Thailand and fault levels would probably be low ie. less than 1.5kA. That 2 pole knife switch is unfused.

Next will the source of supply be able to accomodate the peak load of the residence? The max demand what is it in amps? Peak load is less than the calculated max demand.

Would recommend that the MEN system be implemented ( link at main neutral link to earth bar) then only socket outlets require RCD protection.

Do NOT do this under any circumstances unless you KNOW that MEN has been implemented in your village!! Leave it as TT, most circuits are RCD'd anyway, moving the aircons to the protected side of the 60A RCD would improve safety somewhat.

Electau, examine what will happen in the event of an open neutral between you and the Tx if yours is the only N-E link.

Agree with the replacement of the knife switch, but since the home is already wired there's little point in reducing the CSA of the existing wiring.

The MEN link was only a recomendation, Yes a risk assessment should be carried out first and be subject to PEA approval. As this is a village electrical installation the TT is preferred. MEN connections require polarity testing which is unlikely to be carried out by the person connecting the installation to supply.

Consumers mains 10sqmm 2 core.

Colour codes. Black is line or active, White or grey is neutral. Retain this colour code.

2 pole knife switch should be replaced with a 50 or 63A 2 pole MCB.

The 4sqmm circuits should be protected by 32A MCBs

The 20 amp shower heater should be protected by a 25A or 32A MCB 4 sq mm.

Protection of socket outlets should be 20A wired in 2.5sqmm. RCD protected.

Shower heater area 4 should be protected by a 20A MCB wired in 2.5sqmm.

You will have DSBs ( load centres) in each of the Areas 1 to 6?

The 60A and 30A " safety breaker switch" are MCBs with a fault current rating of 1.5kA. used as an equipment isolating and protective device.

Earthing. All exposed conductive parts of electrical equipment must be earthed to the earth bar not to the main earth electrode.

The main earth is run from the main earth bar to the earth electrode. Main earth minimum 4sqmm.

All other earth conductors 2.5sqmm.

Earthing of steel framework minimum 4sqmm to main earth bar.

Electrical equipment means socket outlets, heaters, airconditioners etc.

The earthing arrangement at present is TT or direct, therefore all final subcircuits must be RCD protected.

Would recommend that the MEN system be implemented ( link at main neutral link to earth bar) then only socket outlets require RCD protection. Otherwise retain the TT system.

Install the neutral link on the line (supply) side of the main switch.

Multimeter on ohms setting, one probe to earth connection on wall socket and the other to Neutral point on the wall socket.

OK, so you're likely just measuring the resistance of your MEN link. Actually nothing wrong with that as this is the path current will take in the event of an L - E fault.

To verify the efficiency of your local ground stake make the measurement from the disconnected stake to your neutral (which should be solidly grounded at the transformer).

That will be anything from 50 ohmsto over 1000 ohms depending on soil conditions. Not required if the MEN system is used. RCDs must be used if the earthing is TT or direct. Based on an electrode depth of 1.2 or 1.8M.

Just to clarify the above post.

PVC/PVC is PVC sheathed PVC insulated. circular cable.

SWA is single wire armoured, requires a cable gland and earthing of armouring.

Forgive me just trying to get things straight, I am not overly worried about my wiring but still have a thirst for knowledge.

I get a reading of just less than 2 ohms on an earth test, with one 1.8 m rod ( can't get longer around here maybe I could order from somewhere ).

So if I get another 1.8m rod link it 1.8m away with 10mm wire to the first one, I will be improving the earth situation, I take it.

The 2 ohms is measured from the main earth connection at the electrode to any point in the installation.

The earth electrode 12.7mm copper clad steel is regarded as having sufficient contact area with the soil.

With the MEN system negligable current flows in the main earth conductor and may be disregarded.

16sqmm PVC/PVC V75 copper. for a 2.5% voltage drop.

If buried directly in the ground cable should be protected from damage. It is better to run in conduit.

Alternatively SWA/PVC/PVC.this does not require mechanical protection.

Cables under TIS standards are rated at 70C.

SWA cables are much more expensive and may not warrant the cost.

Sustained low voltage eg voltages below the normal nominal voltage ranges to the consumers terminals or point of supply are usually caused by.

1. Fault conditions on tthe HV distribution network, eg. loss of one phase.

2. Poor voltage regulation at peak load periods. 1. Distribution network, or 2. LV distribution network.

Low voltage of short duration ( transient events) usually may be caused by the following.

1. Operation of auto circuit reclosers on a HV distribution network.

2. Switching on the HV network.

3. Intermittent heavy loads eg motor starting, welders etc.on the LV distribution system.

Reduction of voltage by system operators on an HV system is not carried out.System operators will shed load or load will be shed automatically by protective devices on the HV system

With a typical Delta-Wye residential transformer, the loss of a HV primary fuse will cause low voltage on two secondary phases.

With a delta HV and star LV when there is loss of one HV phase the voltage on the LV will be,

LV eg. A phase to neutral 220V

B phase to neutral 220V

C phase to neutral 155V. ie 220/1.414.

A phase to B phase 380V.

B phase to C phase 0 volts.

C phase to A phase 0 volts.

Two phases to neutral are still available to maintain a limited supply.

I disagree! You maybe trying to say that a blown primary fuse creates an open-delta condition, which it does not, but then the voltages you claim make no sense. With a blown primary fuse the magnetic flux in two of the three transformer windings (cores) is significantly reduced by approximately 50%, therefore you cannot have normal 220V on those two secondary phases.

You are quite correct, one forgot that on the delta side there was a V connection caused by the lost phase supply.

A to N 220. B to N 155 C to N 155.

Generally a supply authority will approve a 3 phase supply on the following.

1. Type of consumer. Residential. Commercial etc.

2. Load and maximum demand of consumer.

3. Type of electrical load. eg 3 phase motors.

4. Where single phase supply may cause undue voltage drop and affect other consumers. eg rural areas.

Loss of supply on one phase is not a reason for connecting a 3 phase 4 wire supply. Loss of a HV fuse will cause one phase to fall to 220/1.414 volts. to neutral.

With a typical Delta-Wye residential transformer, the loss of a HV primary fuse will cause low voltage on two secondary phases.

With a delta HV and star LV when there is loss of one HV phase the voltage on the LV will be,

LV eg. A phase to neutral 220V

B phase to neutral 220V

C phase to neutral 155V. ie 220/1.414.

A phase to B phase 380V.

B phase to C phase 0 volts.

C phase to A phase 0 volts.

Two phases to neutral are still available to maintain a limited supply.

Generally a supply authority will approve a 3 phase supply on the following.

1. Type of consumer. Residential. Commercial etc.

2. Load and maximum demand of consumer.

3. Type of electrical load. eg 3 phase motors.

4. Where single phase supply may cause undue voltage drop and affect other consumers. eg rural areas.

Loss of supply on one phase is not a reason for connecting a 3 phase 4 wire supply. Loss of a HV fuse will cause one phase to fall to 220/1.414 volts. to neutral.

Individual residential electrical installations do not generally require a 3 phase supply.

Multi unit blocks will have a 3 phase supply to the main switchboard and single phase to each unit, balanced as far as practicably accross the three phases and neutral.

Insulation values are measured in Megohms. Insulation tests are normally carried out at 500VDC using an approved insulation tester (Megger)

Continuity of earthing conductors are measured in ohms.

Max resistance of a main earth is 0.5ohms.

Max resistance from the main earth connection at the electrode to any part of an electrical installation should not be more than 2 ohms in practice.

The minimum depth of an electrode should not be less than 1.2metres.

A multi meter set on the low ohms range will measure continuity.

With a TT (or direct earthing system) RCDs must be used as a protective device.

With regard to post #14 by sezze.

RCDs are generally 10mA or 30mA and are of fixed setting (IEC). However adjustable units (TIS) are available in Thailand from 5mA to 30mA.

RCDs are available in 300mA but they are not used for the protection of persons.They are used for protection of equipment only.

Here is the official DIAC website which gives information on immigration fraud.

http://www.immi.gov....igration-fraud/

All prospective applicants for an Australian visa should read the information provided.

In reply to post #14.

If correct polarity tests are carried out switching in the neutral conductor only will not occur, as this is part of the testing and verification process when connecting an installation, additions, or repairs to an electrical installation.

1 Visual checks.

2.Earthing.

3.Insulation

4.Polarity tests.

Above are some of the tests required.

If a defect is found it is rectified immediately.

However these tests are not carried out in Thailand so serious defects can and do occur in electrical installations.

An earthing conductor, or a conductor coloured green or green /yellow must never be used as a current carrying conductor in normal operation and a switch must never be connected in an earthing conductor.

What is your proposed max demand?

System of earthing MEN or TT.

What is the route length from point of supply to your main switchboard?

The route length to each guest room from your main switchboard.

Sub board (DSB) in each guest room, single phase to each room.

Max demand of each DSB.

Proposed size of sub mains to each DSB.

What is your proposed voltage drop as a percentage on your consumers mains and submains?

Do those calculations first before purchasing cable.

You should be able to get cut lengths of 50sqmm, you should price 4x 50sqmm circ (one length) against 4 x single core 50 sqmm copper.( individual lengths).

Here is my recent dealings with Thai Embassy in KL - Submitted yesterday, collected today...

No hotel booking required and also obtained a double entry

http://www.thaivisa....t-visa-from-kl/

This is a very good example for a TR application outside of Australia.

Applied in person (not through an agent) at the Thai embassy KL.

Australian citizen.

Now compare this application with other consulates and embassies adjacent or near Thailand.

Your citizenship may be very important in applying for a tourist visa to Thailand.

Yep I just made a post regarding this crossing of neutral and line wires when wiring up the panel in another thread, it is a common, dangerous and potentially deadly practice here due to not having a proper ground which would prevent such incompetence from occurring being as they would dead short immediately if they were so wired. Instead now they just shock you by running voltage backwards through switches and the like so that the switch just disconnects the neutral line instead of the power line energizing everything downstream....

An earthing system will not be affected if the line and neutral are reversed on a TT system as there is no connection between the neutral and main earth.

On an MEN system the neutral is earthed and reversal of the line and neutral will cause the earthing system to rise in potential (voltage). It is limited by an effective main earth and electrode. Automatic disconnection does not occur. This is a potentially hazardous situation.

On a final subcircuit with an MEN system the line and neutral are reversed the neutral will be switched which may cause a hazardous situation as the equipment connected is not isolated from supply if the switch is operated.

A switch must operate in the line conductor only unless the line and neutral are switched simultanously on a final subcircuit from a switchboard.

The problem will not occur if correct polarity tests are carried out initially.

With reference to post #494.

The interpretation was based on the following.

1. That I am an Australian citizen.

2. Australia is one of the countries that is permitted 30 day visa free entry into Thailand.

3. The requirements for a 60 day tourist visa have not changed.

4. That one lodges the application at a Thai Embassy or Consulate in Australia.

Applications at a Thai Embassy or Consulate in a country outside of Australia where the applicant is not a citizen or has permanent residence the new requirements may well apply.

So in Cambodia, at Phnom Penh, an Australian applicant would have to comply with local requirements for a 60 day tourist visa for Thailand.

The same would apply to applicants from the US,UK, Canada, NZ etc.

Have a look and read carefully the original advice posted from the MFA in post number 1.

http://www.mfa.go.th...01.php?&id=2815

The only countries mentioned are listed, These are the ones affected by the changes.

Those countries are required to provide five photos/applications rather than just one that all other countries would be required to provide - the application procedure applies to all countries.

Citizens of following countries are required to provide 5 photos and 5 copies of application form

If you are a national of countries that can obtain a visa free entry (30day) the requirements for a 60 day tourist visa will not have changed for you if you apply in your home country.

If you intend to apply in a third country for a 60 day tourist visa find out the requirements if possible of that particular embassy or consulate first, before applying.

That seems to be the basic interpretation of the requirement.

And there are about 39 countries that have visa free entry for 30days.

Have a look and read carefully the original advice posted from the MFA in post number 1.

http://www.mfa.go.th/web/2501.php?&id=2815

The only countries mentioned are listed, These are the ones affected by the changes.

Australia/NZ.

Switches. C-1 or C-2. ON/OFF, used as a normal switch or as a two way switch. Switch may have a looping terminal for a neutral.

Intermediate switch. position 1. 1-3, 2-4. position 2. 1-4, 2-3.

With intermediate switching the first and last switches are 2 way switches, the others inbetween are intermediate type.

Source. Clipsal, HPM, PDL.